The invention relates to a device for measuring AC currents in the form of a current sensor according to the preamble of claim 1.
Inductive measuring procedures according to the Rogowski principle are known in the area of current measuring technology. In the known models, the current-carrying conductor is routed through a coil. The sensor coil can vary in design. One design was described in DE 195 05 812 C2, in which an electrically insulating annular element is provided as the winding carrier. However, the disadvantage to this design is that production requires numerous different steps. Another disadvantage is that, when setting up a current sensor with an integrated electronic evaluation or calculation circuit, the coil in the form described in DE 195 05 812 C2 as a component in addition to the electronic components of the evaluation or calculation circuit have to be placed, secured and electrically connected. Therefore, the integration of this coil into an electronic evaluation or corrective calculation circuit is associated with a high space requirement and high costs for manufacturing the device as a whole. The additional requirement that sensors be miniaturized to make increasingly smaller models tailored to the respective application available cannot be met with a current acquisition coil according to DE 195 05 812 C2. In the description of another design according to U.S. Pat. No. 5,414,400, the coil is fabricated directly on a printed circuit board using the printed conductors and through platings. Viewed in a radial direction, the printed circuit board segment between the through platings forms the electrically insulating annular element or annular segment. The printed conductors are oriented in such a way that the respective printed conductor on the top of the printed circuit board ends in a through plating for establishing an electrical connection with a printed conductor on the bottom, while the latter in turn ends in a through plating for establishing an electrical connection with an additional printed conductor on the top, thereby representing a winding around the insulating annular segment. The geometric orientation of the printed conductors yields a coil-like winding of the insulating annular segment, which, in its entirety, results in a current acquisition coil according to the Rogowski principle. The key disadvantage to the design described in U.S. Pat. No. 5,414,400 is that the current-carrying conductor must also be routed through the borehole enveloped by the coil. As a result, a current acquisition coil given this design cannot be placed around a current-carrying conductor for purposes of current acquisition at a later time. Another disadvantage is that the coil as designed has a go-and-return type of winding. It is proposed that the current acquisition coil be built around a two-layer printed circuit board, whose windings are quite symmetrically arranged over the entirety, but the individual windings alternate in dimensions. This disadvantage stems from the geometric requirement that the windings for practically two coils lying one inside the other be flatly accommodated on a printed circuit board.
The object of the invention is to realize an inexpensive, compact design for a device for measuring AC currents by means of a current acquisition coil based on a printed circuit board or a printed circuit board segment according to the Rogowski principle, which can at a later point be placed around and encompass the current-carrying conductor without interrupting the function of the current-carrying conductor. The structure of the windings must be very symmetrical in order to achieve a high measuring accuracy.
The object is achieved according to the invention by virtue of the features cited in claim 1.
The device according to the invention for a current acquisition coil is realized with the help of a printed circuit board, which can be flipped open in such a way that the current-carrying conductor to be measured can be inserted in the provided area of the coil without interrupting or deactivating the current-carrying conductor. The opened device for a current acquisition coil is closed for measurement in such a way that the current-carrying conductor is completely enclosed by the current acquisition coil, and the current acquisition coil can measure the current of the current-carrying conductor according to the Rogowski principle. To satisfy additional requirements on the current acquisition coil relating to symmetrical structure or compactness, a multi-layer printed circuit board must be used. This offers more ways in which to control the printed conductor, and enables the most symmetrical structure possible for the current acquisition coil winding.
The printed circuit board of the device for measuring AC currents is dimensioned in such a way that additional electronic components of an evaluation unit can be arranged thereupon. Relative to prior art, this makes it possible as a whole to dimension on a smaller scale and be more cost effective. The evaluation unit can perform a measured value conversion for conditioning measured value signals for open-loop and closed-loop controllers, running comparisons with limiting values and generating xe2x80x9ctoo-lowxe2x80x9d or xe2x80x9ctoo-highxe2x80x9d messages, or for other applications.
The multi-layer printed circuit board structure results in a symmetrical design for the individual windings. In this case, the windings of the coil segment for the first winding direction are arranged on two layers for the printed conductors provided exclusively for this coil segment. With respect to the windings of the coil segment for the second winding direction, e.g., return direction, there are two layers of printed conductors provided exclusively for this coil segment. This makes more free space available for the geometric configuration of the printed conductors.
The invention will be described based on an embodiment and the accompanying figures below.